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NOMMU: Make mmap allocation page trimming behaviour configurable.

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NOMMU mmap allocates a piece of memory for an mmap that's rounded up in size to
the nearest power-of-2 number of pages.  Currently it then discards the excess
pages back to the page allocator, making that memory available for use by other
things.  This can, however, cause greater amount of fragmentation.

To counter this, a sysctl is added in order to fine-tune the trimming
behaviour.  The default behaviour remains to trim pages aggressively, while
this can either be disabled completely or set to a higher page-granular
watermark in order to have finer-grained control.

vm region vm_top bits taken from an earlier patch by David Howells.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Mike Frysinger <vapier.adi@gmail.com>
This commit is contained in:
Paul Mundt 2009-01-08 12:04:47 +00:00 committed by David Howells
parent 8feae13110
commit dd8632a12e
5 changed files with 90 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
Documentation/nommu-mmap.txt
View File

@ -248,3 +248,18 @@ PROVIDING SHAREABLE BLOCK DEVICE SUPPORT
Provision of shared mappings on block device files is exactly the same as for
character devices. If there isn't a real device underneath, then the driver
should allocate sufficient contiguous memory to honour any supported mapping.
=================================
ADJUSTING PAGE TRIMMING BEHAVIOUR
=================================
NOMMU mmap automatically rounds up to the nearest power-of-2 number of pages
when performing an allocation. This can have adverse effects on memory
fragmentation, and as such, is left configurable. The default behaviour is to
aggressively trim allocations and discard any excess pages back in to the page
allocator. In order to retain finer-grained control over fragmentation, this
behaviour can either be disabled completely, or bumped up to a higher page
watermark where trimming begins.
Page trimming behaviour is configurable via the sysctl `vm.nr_trim_pages'.

18
Documentation/sysctl/vm.txt
View File

@ -38,6 +38,7 @@ Currently, these files are in /proc/sys/vm:
- numa_zonelist_order
- nr_hugepages
- nr_overcommit_hugepages
- nr_trim_pages (only if CONFIG_MMU=n)
==============================================================
@ -348,3 +349,20 @@ Change the maximum size of the hugepage pool. The maximum is
nr_hugepages + nr_overcommit_hugepages.
See Documentation/vm/hugetlbpage.txt
==============================================================
nr_trim_pages
This is available only on NOMMU kernels.
This value adjusts the excess page trimming behaviour of power-of-2 aligned
NOMMU mmap allocations.
A value of 0 disables trimming of allocations entirely, while a value of 1
trims excess pages aggressively. Any value >= 1 acts as the watermark where
trimming of allocations is initiated.
The default value is 1.
See Documentation/nommu-mmap.txt for more information.

1
include/linux/mm_types.h
View File

@ -106,6 +106,7 @@ struct vm_region {
unsigned long vm_flags; /* VMA vm_flags */
unsigned long vm_start; /* start address of region */
unsigned long vm_end; /* region initialised to here */
unsigned long vm_top; /* region allocated to here */
unsigned long vm_pgoff; /* the offset in vm_file corresponding to vm_start */
struct file *vm_file; /* the backing file or NULL */

14
kernel/sysctl.c
View File

@ -82,6 +82,9 @@ extern int percpu_pagelist_fraction;
extern int compat_log;
extern int latencytop_enabled;
extern int sysctl_nr_open_min, sysctl_nr_open_max;
#ifndef CONFIG_MMU
extern int sysctl_nr_trim_pages;
#endif
#ifdef CONFIG_RCU_TORTURE_TEST
extern int rcutorture_runnable;
#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
@ -1102,6 +1105,17 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec
},
#else
{
.ctl_name = CTL_UNNUMBERED,
.procname = "nr_trim_pages",
.data = &sysctl_nr_trim_pages,
.maxlen = sizeof(sysctl_nr_trim_pages),
.mode = 0644,
.proc_handler = &proc_dointvec_minmax,
.strategy = &sysctl_intvec,
.extra1 = &zero,
},
#endif
{
.ctl_name = VM_LAPTOP_MODE,

65
mm/nommu.c
View File

@ -10,7 +10,7 @@
* Copyright (c) 2000-2003 David McCullough <davidm@snapgear.com>
* Copyright (c) 2000-2001 D Jeff Dionne <jeff@uClinux.org>
* Copyright (c) 2002 Greg Ungerer <gerg@snapgear.com>
* Copyright (c) 2007 Paul Mundt <lethal@linux-sh.org>
* Copyright (c) 2007-2008 Paul Mundt <lethal@linux-sh.org>
*/
#include <linux/module.h>
@ -66,6 +66,7 @@ atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0);
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
int sysctl_nr_trim_pages = 1; /* page trimming behaviour */
int heap_stack_gap = 0;
atomic_t mmap_pages_allocated;
@ -455,6 +456,8 @@ static noinline void validate_nommu_regions(void)
last = rb_entry(lastp, struct vm_region, vm_rb);
if (unlikely(last->vm_end <= last->vm_start))
BUG();
if (unlikely(last->vm_top < last->vm_end))
BUG();
while ((p = rb_next(lastp))) {
region = rb_entry(p, struct vm_region, vm_rb);
@ -462,7 +465,9 @@ static noinline void validate_nommu_regions(void)
if (unlikely(region->vm_end <= region->vm_start))
BUG();
if (unlikely(region->vm_start < last->vm_end))
if (unlikely(region->vm_top < region->vm_end))
BUG();
if (unlikely(region->vm_start < last->vm_top))
BUG();
lastp = p;
@ -536,7 +541,7 @@ static void free_page_series(unsigned long from, unsigned long to)
/*
* release a reference to a region
* - the caller must hold the region semaphore, which this releases
* - the region may not have been added to the tree yet, in which case vm_end
* - the region may not have been added to the tree yet, in which case vm_top
* will equal vm_start
*/
static void __put_nommu_region(struct vm_region *region)
@ -547,7 +552,7 @@ static void __put_nommu_region(struct vm_region *region)
BUG_ON(!nommu_region_tree.rb_node);
if (atomic_dec_and_test(&region->vm_usage)) {
if (region->vm_end > region->vm_start)
if (region->vm_top > region->vm_start)
delete_nommu_region(region);
up_write(&nommu_region_sem);
@ -558,7 +563,7 @@ static void __put_nommu_region(struct vm_region *region)
* from ramfs/tmpfs mustn't be released here */
if (region->vm_flags & VM_MAPPED_COPY) {
kdebug("free series");
free_page_series(region->vm_start, region->vm_end);
free_page_series(region->vm_start, region->vm_top);
}
kmem_cache_free(vm_region_jar, region);
} else {
@ -999,6 +1004,10 @@ static int do_mmap_shared_file(struct vm_area_struct *vma)
int ret;
ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
if (ret == 0) {
vma->vm_region->vm_top = vma->vm_region->vm_end;
return ret;
}
if (ret != -ENOSYS)
return ret;
@ -1027,11 +1036,14 @@ static int do_mmap_private(struct vm_area_struct *vma,
*/
if (vma->vm_file) {
ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
if (ret != -ENOSYS) {
if (ret == 0) {
/* shouldn't return success if we're not sharing */
BUG_ON(ret == 0 && !(vma->vm_flags & VM_MAYSHARE));
return ret; /* success or a real error */
BUG_ON(!(vma->vm_flags & VM_MAYSHARE));
vma->vm_region->vm_top = vma->vm_region->vm_end;
return ret;
}
if (ret != -ENOSYS)
return ret;
/* getting an ENOSYS error indicates that direct mmap isn't
* possible (as opposed to tried but failed) so we'll try to
@ -1051,23 +1063,25 @@ static int do_mmap_private(struct vm_area_struct *vma,
if (!pages)
goto enomem;
/* we allocated a power-of-2 sized page set, so we need to trim off the
* excess */
total = 1 << order;
atomic_add(total, &mmap_pages_allocated);
point = rlen >> PAGE_SHIFT;
while (total > point) {
order = ilog2(total - point);
n = 1 << order;
kdebug("shave %lu/%lu @%lu", n, total - point, total);
atomic_sub(n, &mmap_pages_allocated);
total -= n;
set_page_refcounted(pages + total);
__free_pages(pages + total, order);
/* we allocated a power-of-2 sized page set, so we may want to trim off
* the excess */
if (sysctl_nr_trim_pages && total - point >= sysctl_nr_trim_pages) {
while (total > point) {
order = ilog2(total - point);
n = 1 << order;
kdebug("shave %lu/%lu @%lu", n, total - point, total);
atomic_sub(n, &mmap_pages_allocated);
total -= n;
set_page_refcounted(pages + total);
__free_pages(pages + total, order);
}
}
total = rlen >> PAGE_SHIFT;
for (point = 1; point < total; point++)
set_page_refcounted(&pages[point]);
@ -1075,6 +1089,7 @@ static int do_mmap_private(struct vm_area_struct *vma,
region->vm_flags = vma->vm_flags |= VM_MAPPED_COPY;
region->vm_start = (unsigned long) base;
region->vm_end = region->vm_start + rlen;
region->vm_top = region->vm_start + (total << PAGE_SHIFT);
vma->vm_start = region->vm_start;
vma->vm_end = region->vm_start + len;
@ -1110,6 +1125,7 @@ error_free:
free_page_series(region->vm_start, region->vm_end);
region->vm_start = vma->vm_start = 0;
region->vm_end = vma->vm_end = 0;
region->vm_top = 0;
return ret;
enomem:
@ -1401,7 +1417,7 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
npages = (addr - vma->vm_start) >> PAGE_SHIFT;
if (new_below) {
region->vm_end = new->vm_end = addr;
region->vm_top = region->vm_end = new->vm_end = addr;
} else {
region->vm_start = new->vm_start = addr;
region->vm_pgoff = new->vm_pgoff += npages;
@ -1418,6 +1434,7 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
vma->vm_region->vm_pgoff = vma->vm_pgoff += npages;
} else {
vma->vm_region->vm_end = vma->vm_end = addr;
vma->vm_region->vm_top = addr;
}
add_nommu_region(vma->vm_region);
add_nommu_region(new->vm_region);
@ -1454,10 +1471,12 @@ static int shrink_vma(struct mm_struct *mm,
down_write(&nommu_region_sem);
delete_nommu_region(region);
if (from > region->vm_start)
region->vm_end = from;
else
if (from > region->vm_start) {
to = region->vm_top;
region->vm_top = region->vm_end = from;
} else {
region->vm_start = to;
}
add_nommu_region(region);
up_write(&nommu_region_sem);